1. Field of the Invention
The present invention relates to a developing device, in which electrostatic latent images on the image carrier are developed using a non-magnetic one component developing agent, a process unit, and an image forming apparatus.
2. Description of the Related Art
In a developing device of this type, if a large quantity of toner as developing agent accumulates on the developing agent supply member, such as a supply roller or the like, various types of problems can occur due to agglomeration of the toner as a result of the pressure due to the self weight. Therefore, normally a second housing chamber that houses a large quantity of toner is provided to the side of and separate from the developing agent supply member or a first housing chamber that houses toner. By gradually supplying an appropriate amount of toner from the second housing chamber to the first housing chamber, agglomeration of toner around the toner supply member is reduced. In the second housing chamber, which houses a large quantity of toner, agglomeration is reduced by mixing the toner with air by agitating the toner using an agitating rotating member such as an agitator or the like.
On the other hand, in color image forming apparatus in recent years, in order to achieve high print speeds, the so-called tandem configuration has been widely adopted. In the tandem configuration, a plurality of a combination of latent image carrier, such as a photosensitive member or the like, and a developing device for developing the latent image on the surfaces of the photosensitive member is disposed in a line, and single color images each with mutually different colors developed on the photosensitive members are transferred onto an intermediate transfer belt or similar, and superimposed. Then, by transferring this superimposed image, multi-color images such as full color images are formed. In this configuration, the combinations of latent image carrier and developing device are aligned in the horizontal direction. Therefore, if a second housing chamber disposed to the side of the first housing chamber is used, it is necessary to provide a considerable amount of space in the horizontal direction. As a result, the apparatus becomes larger.
If a developing device that is long in the vertical direction, as for example the device disclosed in Japanese Patent Application Laid-open No. 2001-194883, is used, it is possible to minimize the increase in size of this type of apparatus. Specifically, on top of the first housing chamber, which includes a supply roller as toner and developing agent supply member, there is a hopper as the second housing member. The toner housed within the hopper drops into the first housing chamber via a connecting aperture provided between the hopper and the first housing chamber. Within the first housing member, the supply roller, which carries toner on its peripheral surface, is rotated, to supply the toner on the supply roller to a developing roller as developing agent carrier. In this configuration, the second housing chamber, which takes up a particularly large amount of space, is provided above the first housing chamber within the developing device. As a result, overall the developing device has a shape that is tall and takes up more space in the vertical direction than in the horizontal direction, so it is possible to minimize the increase of space in the horizontal direction. However, in the developing device according to this configuration, toner that drops from the hopper into the first housing chamber accumulates in large quantities on the supply roller, which is the developing agent supply member. Then the toner agglomerates due to the pressure of the self weight, the torque of the supply roller increases, image density unevenness is caused, and wear of the supply roller is significantly increased.
According to tests carried out by the four inventors, agglomeration of toner within tall developing devices is particularly significant between the supply roller and an opposing side wall surface, of a plurality of side walls of the first housing chamber, when the intervening gap is small relative to the peripheral surface of the supply roller. Specifically, in the developing device with a tall configuration as disclosed in Japanese Patent Application Laid-open No. 2001-194883, after the toner that has accumulated above the supply roller has been carried on the surface of the supply roller, the toner is transported by the rotation to the supply position, which is the portion in contact with or in opposition to the developing roller. Then, the surface of the supply roller that has passed the supply position is again brought into the contact position with the accumulated toner by the rotation. In the space around the area of the supply roller from the supply position to the contact position, the toner moves in the direction of the gravitational force due to self-weight or spreads to the side, and is unable to make good contact with the supply roller, and remains accumulated there. Therefore, if the space referred to above is provided, the amount of wasted toner that is not used in developing increases. Therefore, in tall developing devices, preferably the facing side wall of the first housing chamber in opposition to the area of the supply roller from the supply position to the contact position is brought closer to the supply roller so that waste of toner does not occur.
The developing device disclosed in Japanese Patent Application 2001-194883, and the tall developing device used in the tests by the four inventors of the present invention, were configured as follows. The pressure of the toner that drops from the hopper into the first housing chamber and accumulates on the supply roller increases due to the increase in amount accumulated, so after being pressurized by the toner from the hopper, the toner enters the gap between the supply roller and the opposing side wall of the first housing chamber. The movement of the toner that enters the small gap is restricted, so it is difficult to escape from the gap. On the one hand, toner accumulated on the supply roller can easily enter the gap, so the pressure of the toner within the gap gradually increases, and eventually becomes an agglomerated mass. The torque of the supply roller is increased by the pressure of the agglomerated mass against the supply roller, so image density unevenness becomes worse, and wear of the supply roller occurs.
In recent years the use of toner containing wax within the particles in order to achieve oil-less fixing and low temperature fixing has increased, so these problems can easily arise. The toner is comparatively soft, and the adhesive forces between particles are comparatively large, so agglomerated masses are easily formed.